As techniques relating to conventional video information recording device, video information recording method, video information recording program, and recording medium containing the video information recording program for receiving video information sent by individual or broadcast transmission using various types of cable or wireless networks to record the received video information, there is a moving picture coding system converting device described, for example, in Patent Document 1 specified below.
FIG. 8 shows a view schematically showing the configuration of a conventional moving picture coding system converting device 900, and FIG. 9 shows a procedure when the conventional moving picture coding system converting device 900 performs coding system conversion. Only the portions directly relating to the invention are shown in FIG. 8 and all the rest is omitted.
The conventional moving picture coding system converting device 900 first receives broadcasted video information at a reception unit 901 (S901). Subsequently, a channel selection and decoding unit 904 channel-selects program contents from the received video information and decodes the selected program contents (S902). Subsequently, a control unit 902 encodes the channel-selected and decoded program contents into the MPEG-2 format (S903), and records the program contents 941 encoded in the MPEG-2 format into a recording unit 903 (S904).
The format in this instance is not necessarily limited to the MPEG-2 format, and program contents 942 encoded in the MPEG-4 format can be recorded into the recording unit 903, or both the program contents 941 encoded in the MPEG-2 format and the program contents 942 encoded in the MPEG-4 format may be recorded into the recording unit 903.
However, there is a case where both the program contents 941 encoded in the MPEG-2 format and the program contents 942 encoded in the MPEG-4 format cannot be recorded into the recording unit 903 for reasons of copyright management, problems arising from a capacity of the recording unit 903 or the like, and in such a case, the contents in either one format alone are recorded into the recording unit 903.
Also, in this instance, the program contents in each format may be encoded with the use of an encryption and decryption key 944 and then recorded into the recording unit 903. The encryption and decryption key may be different from program contents to program contents or shared by several program contents. Also, a common key may be used for encryption and decryption, or different keys may be used for encryption and decryption.
Herein, a case is examined where the program contents 941 are used in a device 931 other than the moving picture coding system converting device 900 in which the program contents 941 are recorded. Assume that the moving picture coding system converting device 900 has recorded only the program contents 941 encoded in the MPEG-2 format in the recording unit 903 for reasons of copyright management or any other reason, whereas program contents encoded in the MPEG-4 format alone are available in another device 931.
In such a case, it becomes necessary to convert the program contents 941 encoded in the MPEG-2 format to the program contents 942 encoded in the MPEG-4 format. Accordingly, the control unit 902 in the moving picture coding system converting device 900 reads out the program contents 941 encoded in the MPEG-2 format from the recording unit 903 and decodes the program contents 941 first (S905). The control unit 902 then encodes the decoded program contents into the program contents 942 in the MPEG-4 format (S906).
In this instance, it is possible to encrypt the program contents by various methods at the same time or after a certain time. A key used for encryption can be the same as or different from the encryption and decryption key 944 and various keys can be used. Because this configuration is the same as in the case described above, detailed descriptions are omitted herein.
Subsequently, the control unit 902 writes the program contents 942 in the MPEG-4 format into an SD memory card 922 by way of an input and output unit 905 (S907). The program contents 942 in the MPEG-4 format recorded in the SD memory card 922 can be used in another device 931 (S908).
It should be noted that there is a case where the control unit 902 deletes the program contents 941 encoded in the MPEG-2 format and recorded in the recording unit 903 as soon as it has written the program contents 942 in the MPEG-4 format into the SD memory card 922 by way of the input and output unit 905 in Step S907 for reasons of copyright management or any other reason. Such deletion, however, is not necessarily performed for reasons of copyright management or any other reason.
Patent Document 2 discloses an image information converting device that generates MPEG-4 motion vector information from MPEG-2 motion vector information. When converting encoded data encoded in the MPEG-2 format to encoded data encoded in the MPEG-4 format, this image information converting device reduces a computation amount of motion vector computation by generating MPEG-4 motion vector information from MPEG-2 motion vector information when data of an MPEG-2 P-frame is converted to MPEG-4 P-VOP, and when data of an MPEG-2 I-frame is converted to MPEG-4 P-VOP, by calculating motion vector information of the P-VOP using the motion vector information of the immediately preceding P-VOP.
However, when the program contents 941 in the MPEG-2 format recorded in the former moving picture coding system converting device 900 are used in another device, it is necessary for the moving picture coding system converting device 900 to convert the program contents 941 in the MPEG-2 format to the program contents 942 in the MPEG-4 format. It takes an actual time to convert the program contents 941 in the MPEG-2 format to the program contents 942 in the MPEG-4 format. For example, when the program contents 941 are a one-hour long program, it takes one hour to convert the program contents 941 in the MPEG-2 format to the program contents 942 in the MPEG-4 format. This poses a problem that one hour is necessary to write the program contents 942 in the MPEG-4 format into an SD memory and the user has to wait all the while before he becomes able to use the program contents 942 in another device 931.
Such a problem can be avoided by generating the program contents 942 in the MPEG-4 format in the moving picture coding system converting device 900 and recording the program contents 942 in the recording unit 903 in advance. However, in some cases, it is prohibited to record both the program contents 941 in the MPEG-2 format and the program contents 942 in the MPEG-4 format for reasons of restrictions imposed by copyright management, problems arising from a capacity of the recording unit 903 or the like.
Meanwhile, the latter image information converting device has a problem as follows. FIG. 10 is a schematic view showing a macroblock used for MPEG-2 motion compensation. FIG. 11 is a schematic view showing a macroblock used for MPEG-4 motion compensation. FIG. 12 is a schematic view showing a reference frame for the H.264 standards. As is shown in FIG. 10, motion compensation is performed in the MPEG-2 standards with the use of a macroblock R1 of 16×16 pixels, and as is shown in FIG. 11, because a macroblock in closer color can be searched in the MPEG-4 standards, motion compensation is performed with the use of a macroblock R2 of 8×8 pixels. This means that a used macroblock is different for each coding system.
Also, in the H.264 standards, not only can the motion compensation be performed with the use of a macroblock R3 by setting the immediately preceding frame or the frame of a GOP (Group of Pictures) as the reference frame as is shown in the top row of FIG. 12, but also the motion compensation can be performed with the use of a macroblock R4 by setting frames over a broad range beyond the I-frame as the reference frames as is shown in the bottom row of FIG. 12. Image compression can be therefore performed more effectively. In this case, the conventional motion prediction with the use of a motion vector cannot be performed, and motion prediction has to be performed again.
As has been described, in the motion vector computation in the respective coding systems, such as MPEG-2, MPEG-4, and H.264, the range of reference frames, the unit of motion compensation, with or without the support for arbitrary shape coding are different for each coding system. Hence, the image information converting device is not able to find motion vector information optimized for the coding system after conversion. Consequently, in order to find motion vector information optimized for the coding system after conversion, it is also necessary for the image information converting device to perform motion vector computation again according to the coding system after conversion, and this computation takes a long time.    Patent Document 1: JP-A-9-84011    Patent Document 2: JP-A-2002-152752